Tiantai or T'ien-t'ai (Chinese: 天台; pinyin: PRC Standard Mandarin:Tiāntāi) is an East Asian Buddhist school of Mahāyāna Buddhism that developed in 6th-century China. Drawing from earlier Mahāyāna sources such as Madhyamaka, founded by Nāgārjuna, who is traditionally regarded as the first patriarch of the school, Tiantai Buddhism emphasizes the "One Vehicle" (Ekayāna) doctrine derived from the influential Lotus Sūtra, as well as the philosophy of its fourth patriarch, Zhiyi (538–597 CE), the principal founder of the tradition. Brook Ziporyn, professor of ancient and medieval Chinese religion and philosophy, states that Tiantai Buddhism is "the earliest attempt at a thoroughgoing Sinitic reworking of the Indian Buddhist tradition." According to Paul Swanson, scholar of Buddhist studies, Tiantai Buddhism grew to become "one of the most influential Buddhist traditions in China and Japan."
Tiantai is sometimes also called "The Dharma Flower School" (天台法華宗), after its focus on the Lotus Sūtra, whose Chinese title translates to "Subtle Dharma Lotus Flower Sutra". During the Sui dynasty (581–618), the Tiantai school became one of the leading schools of Chinese Buddhism, with numerous large temples supported by emperors and wealthy patrons. The school's influence waned and was revived again in the Tang by figures like Zhanran, experiencing a second revival period during the Song dynasty. Chinese Tiantai remains a living tradition to this day, being particularly strong in Hong Kong and Zhejiang Province.